The space radiation effects of concern to modern microcircuits are Single-Event Upsets (SEUs) and Total Ionizing Dose (TD). In the SEU effect, cosmic rays and high energy protons, that undergo electronic reactions with the integrated circuits, deposit sufficient charge in memory cells and latches to flip bits and corrupt data. Such events do not induce any physical damage and thus are nondestructive. On the other hand, in the TD effect, gate oxides are charged which is a permanent change. This shifts transistor threshold voltages and reduces the channel mobility. A change in these parameters degrades the performance of CMOS integrated circuits (ICs) by changing the propagation delay.
Radiation sensitive field effect transistors have application as integrating dosimeters providing a measurement of the amount of dose absorbed from various radiation sources. Field effect transistor (FET) dosimeters are advantageous as compared to more conventional dosimeters because FET dosimeters are small and they provide continuous readout. They operate on the principle that ionizing radiation causes a shift in threshold voltage due to the accumulation of trapped charge in the gate oxide and at the oxide interface. Unfortunately, FET dosimeters also suffer from a number of shortcomings. In particular, their sensitivity to radiation is low and their accuracy is diminished by changes in threshold voltage caused by temperature variations. Thus it would be highly desireable to have an FET dosimeter which is relatively insensitive to variations in temperature.